X-ray imaging is a well known and extremely valuable tool for the early detection and diagnosis of various disease states in the human body. The use of contrast agents for image enhancement in medical x-ray imaging procedures is widespread. An excellent background on iodinated and other contrast agents for medical imaging is provided by D. P. Swanson et al, Pharmaceuticals in Medical Imaging, 1990, MacMillan Publishing Company.
Various soluble and water insoluble iodinated amides and esters have been used as x-ray contrast agents. For example, U.S. Pat. No. 3,097,228 describes derivatives of 2,4,6-triiodobenzoyloxyalkanoic acids having the structure ##STR2## wherein R.sup.1 is H or lower alkyl, R.sup.2 is H or alkanoyl, R.sup.3 is H or alkanoylamino, and R.sup.4 is lower alkyl. However, there is no suggestion of a carboxamide group linked to an ester group on an iodinated aromatic ring.
U.S. Pat. No. 4,328,202 describes ionic 5-C-substituted 2,4,6-triiodoisophthalic acid derivatives as x-ray contrast agents, but does not suggest a carboxamide group linked to an ester group on an iodinated aromatic acid.
U.S. Pat. No. 4,364,921 describes triiodinated isophthalic acid diamides as nonionic x-ray contrast media, but does not suggest a carboxamide group linked to an ester group on an iodinated aromatic ring.
EP-A 498,482 describes nanoparticulate x-ray contrast compositions which have proven to be extremely useful in medical imaging. However, particulate contrast agents in certain in vivo applications can exhibit less than fully satisfactory enzymatic degradation, e.g., in plasma and blood.
It would be desirable to provide compounds for use as x-ray contrast agents having improved enzymatic degradability and appropriate solubility profiles.